police fired tear gas near cairo's tahrir square, the heart of the 2011 uprising that toppled hosni mubarak. now thousands of demonstrators are calling for morsi to step down. tara mergener for cbs news, washington. >>> a natural gas explosion destroyed two buildings in one of new england's largest steams of the the blast sent bricks and glass flying through downtown springfield, massachusetts, about 90 miles west of boston. the blast was so loud, it was heard for miles around. >> i jumped. i could feel the garbage cans move next to me. i could hear the windows shaking. automatically -- i knew where it came from, from this part of the city. >> firefighters were investigating a gas leak about 40 minutes before the explosion. some of the injured include firefighters and utility workers, but authorities say there were no fatalities. >>> well, a party train from southern california to las vegas is on the fast track to becoming reality. the las vegas railway express and union pacific railroad have agreed to start working on tracks for what they call the x train. it would make the roundtrip from